Diplodia ear rot (DER) is a widespread fungal disease of corn caused by the pathogens Stenocarpella maydis and Stenocarpella macrospora. DER causes significant damage to crops with loss of yield and decrease in grain quality. In addition, when present in animal feed S. maydis has been associated with diplodiosis, a nervous disorder of livestock. DER has been problematic in many countries including the United States, South Africa, Brazil, Argentina, and Mexico. In South Africa, S. maydis is the most prevalent ear rot pathogen (Flett, B. B. and McLaren, N. W.; Plant Disease 78:587-589 (1994). Symptoms of DER include white fungal mycelium which starts at the base of an ear of corn and may cover the entire ear with pycnidia at the kernel base. Discoloration of kernels is another symptom of DER which may not be evident until kernels are removed from the ear. Symptoms are frequently not observable until the ear is opened. Phenotypic screening for ear rot infection is often difficult due to the need to hand harvest ears. Disease management strategies include such methods as crop rotation and fungicide application. However, genetic resistance to DER is the most promising method of controlling the disease. To date, a need exists in the art to develop improved methods to identify and select for genomic regions associated with tolerance or resistance to DER in order to breed DER resistant plants.
Studies have mapped QTL associated with resistance to other ear rot pathogens such as Fusarium verticilliodes and Fusarium proliferatum, the causative agents of Fusarium ear rot (Ali, M. L. et al., Genome 48: 521-533 (2005)), Fusarium graminearum, the causative agent of Gibberella ear rot (Robertson-Hoyt, L., Crop Sci. 46:1734-1743 (2006)), and Aspergillus flavus, the causative agent of Aspergillus ear rot (Busboom, K. N. and White, D. G., Amer. Phytopathological Soc. 94:1107-1115 (2004)). QTL associated with resistance to diplodia ear rot have not been disclosed before the priority date of this patent application.